In situ combustion process



Jan. 3, 1961 F. w. CRAWFORD 2,967,052

IN SITU COMBUSTION PROCESS Filed March 51. 1958 AIR INJECTION (AIR K ESTRATEJM INVENTOR.

F. W. CRAWFORD ates IN SIT-U COMBUSTIONPROCESS -9 Claims. (Cl. 262-3)This invention relates to .a .process --for ginitiating and effecting insitu combustion .in a carbonaceous stratum.

In situ combustion in the recovery vof hydrocarbons from undergroundstrata containing carbonaceous material is becoming more prevalent inthe petroleum industry. In this technique of production, combustion isinitiated in thecarbonaceous stratum and the resulting combustion zone.is caused to move thru the stratum by either inverse or direct airdrive whereby the heat of combustion of a substantial proportion of thehydrcarbon in the stratum drives out and usually upgrades a substantialproportion of the unburned hydrocarbon material.

The ignition .of carbonaceous material in :a {stratum around a boreholetherein, followed by injection of air thru the ignition borehole andrecovery of product bydrocarbons and combustion gas thru anotherborehole in the stratum, is a direct air .drive process for effecting insitu combustion andrecovery of hydrocarbons from the stratum. ln-thistype of operation .the stratum usually plugs in ;front of the combustionzone "because a heavy viscous liquid bank of hydrocarbon .collects in.the stratum in advance of the combustion zone which .prevents movementof air to the combustion process. :To overcome this difliculty and ,topermit the continued progress of the combustion zone thru thestratum,.inverse .air injection has :been resorted to. By thistechnique, a .combustion zone is established around anignit-ioniborehole by any suitable means and air :iS fed thru thestratum to the combustion zone from one ,ormore surroun ingboreholes- Ineither ;a zdirect or inverse air injection proces-s't'he stratumcontaining the carbonaceous material mustfirst be ignited around :aborehole therein where it is desired t i ti t e combu tion proce Somedifficulty has been experienced in establishing combustion in.thecarbonaceous material around -a borehole because of :the hi h :hea lss s t t e a ja n ro k nds r tum. Various types of theaters have beenutilized ;to.-raise the temperature of the stratum around the ignitionborehole -=to ignition temperature so that the combustion processtakesoff When contacted with Q -containinggas, usually air. This invention isconcerned with a method or process for {simultaneously drilling an{ignition borehole in a. carbonaceous stratum and igniting thestraturnaround the borehole.

It is accordingly an object of the invention to provide an improvedprocess for initiating in situ combustion in a carbonaceous stratumaround a boreho'e therein. Another object of the invention is to providea process for simultaneously drilling a borehole thru a carbonaceousstratum and igniting 1the1 tratum around :the :borehole. Arfurtherobject .is to .provide a process for establishing :in situcombustion ina carbonaceous stratum and simultaneously .initiatingmovement of thecombustion zone thru the formation by inverse air injection. Otherobjects of the-invention will become apparent upon consideration of theaccompanying disclosure.

atent ICE -A :broad .aspect of the invention comprises drilling :aborehole thru a carbonaceous stratum by means of a flame drill andsimultaneously contacting the hot wall of tthetborehole with o-containing gas so as to initiate combustion of .the carbonaceousmaterial adjacent the borehole. The initiation of combustion maybeeifected during any stage of the flame drilling step by contacting thewall of the borehole while at or above ignition temperature withtree-oxygen containing gas, such as air; however, it is preferred tofeed air in excess to .the hot .drilling zone during the early stages of.the drilling so that combustion is initiated in the stratum from .thetop to the bottomsection thereof.

=,Where the term air is utilized herein, it .is to be understood thatother (D -containing gas or gases, such as diluted air or air enrichedwith oxygen, may be utilized inizlieu thereof providing theconcentration of O .is sufli- .cient to initiate and/ or propagatecombustion of the .carbouaceous material.

fDuring thermal or flame .drilling of the carbonaceous stratum air forcombustion of the carbonaceous material may be supplied thru theignition borehole by :suitable conduit means leading to the heated areasuch as thru the drill string or thru .conduit attached to the drillstring.

The preferred method of contacting the heated section of :stratum.during the flame or thermal drilling process comprises injecting airinto .the stratum thru one or more boreholes closely spaced to theignition boreho'e being vdrilled so that the air passes thru the stratumto the hot area around the ignition borehole. .In this manner asignition of the stratum takes place, the resulting com- ;bustion zone is:moved laterally outwardly from the ignition borehole toward theinjection borehole or boreholes. This procedure establishes in situcombustion by inverse air injection simultaneously with the drilling ofthe ignivtion borehole.

The flame drilling of rock and mineral formations is conventional, asillustrated by US. Patents 2,674,993, 2j 693,9 37, and 2,628,817. Animproved thermal drill suitable :for effecting the process of theinvention is disclosed and claimed in the application of Martin AJRyan,S erial No. 515,940, filed June 16, 1955 now Patent No. 2,896,914. Inthe process of these patents the rock in the path of the borehole ismelted and spalled and other- .wise disintegrated into fine particleswhich are blown :out of the borehole by means of the high velocity ofthe .cornbpstion gas from the .burner. The burner -of :theabove-identified application imparts a spiral movement .to the rapidlyexpanding flame gases emanating from the burner, which aids indisintegrating the rock, and is particularly suitable for use in thisinvention.

.Elio illustrate the invention, reference is made to the accompanyingschematic drawing which is an e'evation gin section thru a formationshowing an arrangement of boreholes and apparatus for. eflecting theinvention.

Referring to the drawing, a carbonaceous stratum 10 penetratediby .airinjection borehole 12 and an ignition borehole 514. A flame drill 16 isprovided with an .air line 18and ,a fuel gas line 20. Flame and hotcombustion gas at 22 impinges upon the stratum in the area of 24 toheat, spall .and disintegrate the rock formation below the flame ,drill.'During drilling air is injected thru line :26 and borehole 12 into thestratum 10 from which it travels to borehole 14 where it initiatescombustion of the in-place hydrocarbon material when the temperature ofthe stratum at the ignition well reaches combustion supportingtemperature. During the process combustion gases and produced gases arepassed thru line 28 to suitable recovery equipment.

Well 12 is illustrative of a line of wells or a ring of wells encirclingignition well 14.

The injection of air for the combustion of carbonaceous material duringthe flame drilling of the carbonaceous stratum is preferably effectedthru a ring of injection boreholes surrounding the ignition boreholebeing flame drilled. The injection borehole or boreholes should bespaced a short distance from the ignition borehole within the range of afew feet to 50 feet or more depending upon the permeability of thestratum. Usually the injection boreholes can be effectively spaced adistance of 5 to 25 feet from the ignition borehole. In coal seams andother carbonaceous stratum of extremely low permeability, the processcan be readily efiected by horizontally fracturing the stratum at one ormore selected levels therein by conventional methods such as byhydraulic or other fluid pressure, including air pressure. Thefracturing is effected thru the injection boreholes by packing off theselected level around an injection conduit or Well tubing and applyingfluid pressure to the stratum at the packed olf level thru an outlet inthe tubing until the stratum separates thereby causing fracturing.Propping of the fracture or fractures with sand or other particulatesolid material may be effected in order to keep the fractures open. Whenfracturing with a gas, such as air, alternately increasing anddecreasing pressure rapidly thru the fracturing pressure, afterfracturing has been effected, results in fluttering and creation ofsufficient debris in the fractures to provide propping. However, thespecific fracturing and propping procedure to be utilized is not a partof the invention and further discussion is believed unnecessary.

The invention is also applicable to in-line in situ combustion drivewherein a line of ignition boreholes is drilled only down to the stratumto be produced and, before flame drilling the boreholes thru thestratum, a line of injection boreholes is drilled thru the stratumsubstantially parallel to the line of ignition boreholes and spacedtherefrom sufliciently close to permit injection of air thru the stratumto the line of ignition boreholes with reasonable air injectionpressures. If the permeability of the stratum is low so as to requireexcessive injection pressures, the stratum should be fracturedhorizontally so that the fractures extend toward the ignition boreholesand preferably to the axis of the borehole, particularly, where thecarbonaceous stratum is impermeable as in a vein of bituminous oranthracite coal. It is feasible to simultaneously drill more than one ofthe ignition boreholes with a flame drill thru the carbonaceous stratumand inject air thru the stratum to the flame drilling area or areas soas to initiate combustion in a plurality of the boreholes atsubstantially the same time. It is also feasible to initiate combustionduring flame drilling in the carbonaceous stratum in one borehole at atime until all of the ignition boreholes in the line have been drilledand the area surrounding the same has been ignited.

In one embodiment of the invention two lines of injection boreholes areutilized for injecting air during the flame drilling of the carbonaceousstratum in the several ignition boreholes. In this procedure in-lineinjection boreholes are positioned on opposite sides of the line ofignition boreholes so that the combustion zone is moved radiallyoutwardly from each ignition borehole and from the line of ignitionboreholes toward the injection boreholes on both sides of the line ofignition boreholes. In this manner the recovery of hydrocarbons by insitu combustion is speeded up and is rendered more efficient.

In the various embodiments of the invention thus far described, thepreferred procedure is to drill the ignition boreholes to thepetroliferous bed and set the surface casing in the borehole with orwithout cementing and then proceed with the step of flame drilling thruthe petroiiferous bed while injecting air thru said bed to the hot Wallof the boreholes so as to establish combustion of the petroliferousmaterial.

Certain modifications of the invention will become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations of the invention.

I claim:

1. A process for completing an ignition borehole in a stratum containingcarbonaceous material which comprises drilling a borehole to saidstratum from the surface; drilling from said borehole thru said stratumwith a flame drill by continuously directing a flame into said stratumwhereby said stratum is heated to ignition temperature; andsimultaneously contacting the wall of said borehole within said stratumwith O -containing gas so to initiate combustion of said stratumradially around said borehole.

2. The process of claim 1 wherein said combustion is initiated byinjecting said gas into said stratum thru at least one adjacent boreholeduring the step of drilling with said flame drill so that 0 passes intothe heated zone to ignite said stratum.

3. The process of claim 2 wherein air is injected into said stratum thrua ring of boreholes surrounding said ignition borehole.

4. The process of claim 1 wherein air for combustion of saidcarbonaceous material is injected into said stratum thru said boreholeto initiate combustion and thereafter air is injected into said stratumthru at least one other borehole, whereby said air passes to theresulting combustion zone and moves same countercurrently to flow ofair.

5. The process of claim 1 including the step of moving said flame drillup and down in said borehole within said stratum so as to play saidflame on the wall of said borehole thereby increasing the temperature ofthe surrounding stratum.

6. A process for simultaneously drilling an ignition borehole in acarbonaceous stratum and initiating in situ combustion therein whichcomprises drilling an ignition borehole to an upper section of saidstratum; drilling at least one injection borehole thru said stratumadjacent said first borehole; horizontally fracturing said stratum thrusaid at least one injection borehole to provide at least one fractureextending to the line of said ignition borehole; thereafter drillingsaid ignition borehole thru said stratum with a flame drill bycontinuously directing a flame into said stratum so as to heat the wallthereof to ignition temperature; and while said ignition borehole is atsaid temperature and while continuing flame drilling, injecting air intosaid at least one injection borehole so as to pass air to the hotsection around said ignition borehole and establish in situ combustionin said stratum.

7. The process of claim 6 wherein several injection boreholes ringingsaid ignition borehole are used in fracturing and in air injection so asto advance the resulting combustion zone outwardly from said ignitionborehole.

8. The process of claim 6 wherein a row of in-line ignition boreholesare drilled, a generally parallel row of injection boreholes aredrilled, fracturing is effected thru the injection boreholes, thermaldrilling is efiected in the ignition boreholes, and air is injected thruthe injection boreholes.

9. The process of claim 8 wherein a second line of boreholes on theopposite side of the line of ignition boreholes from said row ofinjection boreholes is also used for fracturing and air injection.

References Cited in the file of this patent UNITED STATES PATENTS2,584,605 Merriam et al. Feb. 5, 1952 2,688,464 Payne Sept. 7, 19522,780,449 Fisher et al. Feb. 5, 1957 2,818,118 Dixon Dec. 31, 19572,833,516 Salomonsson May 6, 1958 2,889,882. Schleicher June 9, 1959

1. A PROCESS FOR COMPLETING AN IGNITION BOREHOLE IN A STRATUM CONTAININGCARBONACEOUS MATERIAL WHICH COMPRISES DRILLING A BOREHOLE TO SAIDSTRATUM FROM THE SURFACE; DRILLING FROM SAID BOREHOLE THRU SAID STRATUMWITH A FLAME DRILL BY CONTINUOUSLY DIRECTING A FLAME INTO SAID STRATUMWHEREBY SAID STRATUM IS HEATED TO IGNITION TEMPERATURE; ANDSIMULTANEOUSLY CONTACTING THE WALL OF SAID BOREHOLE WITHIN SAID STRATUMWITH O2-CONTAINING GAS SO TO